1. Field of the Invention
This invention relates to electro-hydraulic pressure regulating valves.
2. Description of the Prior Art
In mechanical, open-center pressure regulating valves, fluid at a high supply pressure is regulated to a control pressure by a spring biased valve spool which stabilizes in a regulating position wherein all of the supply pressure not consumed by the pressure actuated device or the control pressure circuit is exhausted to a low pressure fluid sump. Plural applications of such valves in the same system are complicated by the fact that each open-center valve consumes all of the supply pressure delivered to it. In open-center electro-hydraulic pressure regulating valves, the principle of operation is the same as in the mechanical valves but the valve spools are exposed to additional modulating pressure chambers into which fluid is introduced at varying modulating or bias pressures under the control of a solenoid valve. The modulating pressure acts either with or against the force of the regulating spring to change the regulated control pressure. In U.S. Pat. No. 3,777,480, issued Dec. 11, 1973 to Donald D. Stoltman and assigned to the assignee of this invention, a gas turbine fuel control is described including a closed-center slave valve which throttles fuel at a high supply pressure to a lower control or nozzle pressure at a rate determined by the magnitude of a bias pressure acting on the slave valve. The slave valve exhausts the nozzle pressure when the bias pressure is reduced to atmospheric pressure. An electro-hydraulic pressure regulating valve according to this invention regulates supply pressure to control pressure in closed-center fashion to conserve supply pressure and embodies a simple arrangement of structural elements particularly suited for miniaturization of the valve.